US President Barack Obama and Republic of Korea's President Park Geun-hye sent a unified message to the Democratic People's Republic of Korea while expressing hope that the crisis there can be resolved with Chinese input.

Also on Tuesday, Bank of China, which is one of the country's biggest banks and has growing operations in the United States, said it has stopped doing business with a DPRK bank that Washington accuses of financing missile and nuclear programs.

Obama, speaking at a joint White House news conference with Park, said the US is "fully prepared and capable of defending ourselves and our allies with the full range of capabilities available, including the deterrence provided by our conventional and nuclear forces".

"The days when North Korea can create a crisis, and enlist concessions, those days are over," he said.

Obama added, however, that both the US and the ROK are prepared to engage the DPRK diplomatically and, over time, build trust. "The burden is on Pyongyang to take meaningful steps to abide by its commitment and obligations, particularly the denuclearization of the Korean Peninsula," he said.

Park said her country and the US won't tolerate "North Korea's threats and provocations", but stressed that Seoul and Washington will work together to encourage Pyongyang to "make the right choice through multifaceted efforts, including the implementation of the Korean Peninsula trust-building process that I had spelled out".

"Should North Korea choose the path to becoming a responsible member of the community of nations, we are willing to provide assistance together with the international community," said Park, who in late February took office as ROK's first female president.

She said China has a role to play in achieving the ultimate goal of the DPRK abandoning its nuclear-weapon ambitions and joining the international community.

"China's role, China's influence, can be extensive," said Park, who speaks Mandarin. A report by the nonpartisan Congressional Research Service issued two weeks ago said the ROK leader appears to be prioritizing improved relations with China, which had cooled during the presidency of her immediate predecessor, Lee Myung-bak. The report also said the emergence of China now influences nearly all aspects of the ROK's foreign and economic policies.

On Tuesday, Park said she and Obama share the view that Beijing's participation in efforts to resolve problems with Pyongyang is important.

"China has taken an active part in adopting UN Security Council resolutions and is faithfully implementing the resolutions," she said, referring to sanctions imposed against the DPRK.

In Beijing, Bank of China said it had notified the Foreign Trade Bank of the DPRK- the country's main foreign-exchange bank - that its accounts were being closed and all transactions suspended. BOC's brief statement didn't include details such as the number of accounts being closed.

In March, the US Treasury Department singled out the Foreign Trade Bank over its alleged role in financing Pyongyang's nuclear program and announced sanctions to cut off the bank and several DPRK officials from the US financial system.

Diplomats have been busy in trying to find a resolution to the crisis that has unfolded since mid-February when the DPRK conducted its third nuclear test and went on to display belligerent behavior that has only recently appeared to subside.

US Secretary of State John Kerry and General Martin Dempsey, chairman of the Joint Chiefs of Staff, visited China, and Wu Dawei, China's special envoy for the Korean Peninsula and chairman of the suspended Six-Party Talks, came to Washington. (The talks involve the ROK, the DPRK, China, the US, Japan and Russia.)

Zbigniew Brzezinski, a former US national security adviser, recently said the DPRK's recent lowering of tensions could be the result of back-channel communication between Pyongyang and Beijing.

On Monday, Western media outlets reported that the DPRK had withdrawn two mobile ballistic missiles from a launch pad on the country's east coast after weeks of speculation that it was planning another missile or nuclear test.

However, on Tuesday, the DPRK issued a warning over this week's joint naval exercises by US and South Korean forces in the Yellow Sea. A statement carried by the official Korean Central News Agency vowed that the country would strike back if "even a single shell drops" onto its territory during the five-day drill, which ends on Friday.

James Schoff, a senior Asia program associate at the Carnegie Endowment for International Peace, said the Korean Peninsula problem cannot be managed effectively without policy coordination with China.

The US and the ROK, he said, "want to see China apply more economic, financial and diplomatic pressure on North Korea and they want China to support tougher sanctions if North Korea continues to violate UN Security Council resolutions".

Scott Snyder, a senior fellow in Korean studies at the Council on Foreign Relations, said it's unclear whether Beijing has taken special measures to try to defuse tensions on the peninsula.

"But the promised midrange-missile exercises that North Korea seemed to be planning as of the second week of April did not materialize, and there's a possibility that they could be postponed for an indefinite period of time," he said.